(1) Field of the Invention
The present invention relates to a transparent article suitable for spectacle lenses, camera lenses and other optical articles, which is excellent in scratch resistance, abrasion resistance, impact resistance, chemical resistance, flexibility, heat resistance, light stability and weatherability and which shows a good light fastness when dyed, and a process for the preparation of this transparent article.
(2) Description of the Prior Art
Plastic articles represented by plastic lenses have very excellent impact resistance and transparency and a light weight and can be easily dyed. Accordingly, demands for such plastic articles are increasing in these days. However, plastic lenses are defective in that they have a lower surface hardness than inorganic glass lenses and they are readily scratched. Furthermore, since the mechanical strength of plastic lenses is lower than that of inorganic glass lenses, the thickness of the central portion of the lens should be increased. Moreover, since the refractive index of plastic lenses is lower than that of inorganic glass lenses, the edge portion is extremely thick especially in case of high-diopter myopia lenses, and outward appearance is bad and wearing is often shunned from the viewpoint of fashion.
Trials to eliminate the above-mentioned defect of the easy-scratching property have been proposed. For example, there are known a method in which an inorganic substance such as SiO.sub.2 is coated on a plastic substrate by vacuum evaporation deposition (see Japanese Unexamined Patent Publication No. 58-204031), and a method in which a polyorganosilane hard coat film or an acrylic hard coat film is formed on the surface of a plastic substrate (see U.S. Pat. Nos. 3,986,997 and 4,211,823, and Japanese Unexamined Patent Publications Nos. 57-168922, 59-38262, 59-51908, 59-51954, 59-78240, 59-8936, 59-102964, 59-109528, 59-120663, 59-155437, 59-174629, 59-193969 and 59-204669). In order to eliminate the latter defect, that is, bad appearance owing to extreme increase of the thickness in the edge portion of a high-diopter lens, increase of the refractive index has been examined and various proposals have been made (see Japanese Examined Patent Publications No. 58-17527 and 58-14449, and Japanese Unexamined Patent Publications 57-28117, 57-54901, 57-102601, 57-104901, 58-18602, 58-72101, 59-87124, 59-93708 and 59-96109).
The conventional technique of improving the surface hardness by vacuum evaporation deposition of an inorganic substance such as SiO.sub.2 can provide a high hardness, but is defective in that the adhesion to the substrate, the heat resistance, the impact resistance, the hot water resistance and the weatherability are degraded. Moreover, this conventional technique has a fatal defect of loss of dyeability, which is one of characteristics of a plastic lens.
The technique of forming a silane or acrylic type hard coat film, as disclosed in Japanese Unexamined Patent Publications No. 59-3826and No. 59-51908, can impart excellent heat resistance, impact resistance and dyeability, but according to this technique, uniform control of the film thickness is difficult and if this technique is applied to a substrate having a refractive index higher than 1.55, an interference band, which is not formed in case of a plastic lens substrate having a refractive index lower than 1.55, is formed because of the difference of the refractive index between the substrate and the hard coat film. This problem can be solved by bringing the refractive index of the hard coat film close to that of the substrate, and Japanese Unexamined Patent Publication No. 57-168922discloses a coating composition comprising an antimony pentoxide sol having a high refractive index and an organic silicon compound. However, this technique has a fatal defect of poor dyeability.
Moreover, as means for improving the surface hardness and the anti-reflection property of plastics, there is known a method in which SiO.sub.2 having about 1 micron thickness is coated on a plastic substrate by vacuum evaporation deposition and a multi-layer anti-reflection film is coated thereon (see Japanese Unexamined Patent Publication No. 56113101)
Furthermore, Japanese Unexamined Patent Publications Nos. 59-48702, 59-78301 and 59-78304 disclose a method in which a polyorganosilane type hard coat film or a cured epoxy resin film is formed on the surface of a plastic substrate and an anti-reflection film composed of an inorganic substance is formed thereon.
The technique disclosed in Japanese Unexamined Patent Publication No. 56-113101 provides a high hardness and a high anti-reflection property, but this technique is defective in that the adhesion, heat resistance, impact resistance, hot water resistance and weatherability are degraded.
The technique disclosed in Japanese Unexamined Patent Publications Nos. 59-48702, 59-78301 and 59-78304 provides a high anti-reflection property, but the technique is defective in that the adhesion to the substrate is insufficient and a deep and wide scratch is readily formed. Moreover, the coating formed according to this technique is readily attached by water, an alcohol or the like, and the adhesion after dipping in hot water and the weatherability are poor.
We have conducted research with a view to solving the foregoing problems, and as the result, we have arrived at the present invention described hereinafter.